The control systems become more and more important in promoting the development of the modern civilization and technology. For example, the home electrical appliances, automobiles, and nightstools in the bathroom are all control systems, which are more popular in industrial application.
For the application of the servomechanism, a mathematics model is first set up according to the physical behavior of the system, whereby the behavior of the system is conveniently predicted and controlled by the use of the control function in the mathematics model.
The traditional Proportional Integral Differential (PID) controller includes the proportional term, the integral term and the differential term, wherein the proportional item is used to tune the output of the controller according to the dimension of the inaccuracy, the integral term is used to dissipate the inaccuracy in steady state, and the differential term is functional for predicting the trend of inaccuracy. The PID controller is still widely used because of its simple structure.
Taking a motor as an example. Please refer to FIG. 1, which is a schematic block diagram of a motor control system according to the prior art.
As shown in FIG. 1, the controlled body 11 in the control system 10 is a motor and its mathematics model is set up based on the physical behavior of the motor operation. The transfer function of the mathematics model is Kt/((Jm+Jd)s+B), wherein Jm is the inertia of the motor, Jd is the inertia of the load, B is a damping coefficient, and Kt is a value of ratio (proportion).
The controlled 11 receives a driving signal PV and accordingly produces an output signal PY, which is a rotational speed in this example. The motor is subject to an outside interference while operating, wherein the interference may result from the effects of electromagnetism or machinery. A third summer 111 is deposed to take the interference into consideration of control system 10, namely, the third summer 111 takes account of the sum of a third operating signal PU3 from a master controller 12 in front and a interfering signal PW to produce a drive signal PV to drive the motor.
The diagram of the conventional motor shown in FIG. 1 has been simplified. To describe more completely, the third operating signal PU3 passes trough a high-frequency electric current circuit and then combines with the interfering signal PW, while the third operating signal PU3 is an equivalent armature electric current and the interfering signal PW is an interfering torque.
The master controller 12 in FIG. 1 is a kind of proportional integral controller. The transfer function of the controller 12 is KP+KI*1/s, which includes a proportional function KP and a integral function KI*1/s. The proportional function KP as a proportional coefficient is for raising the gain bandwidth of an open loop of the control system 10, so as to make the control system 10 to response quickly. The KI is an integral coefficient, which is used to reduce the following error of stable state in the control system 10.
Because the response speed goes faster with the wider target bandwidth Bw of the control system 10, the proportional coefficient KP is set as 2πBw(Jm+Jd)/Kt generally to ensure the gain bandwidth of the open loop will be provided with the target bandwidth Bw.
The master controller 12 receives an error signal PE, and then the error signal PE is processed by the proportional function KP to produce a first operating signal PU1, and processed with by the integral function KI*1/s to generate a second operating signal PU2. The first operating signal PU1 and the second operating signal PU2 are summed by a second summer 121 to output an third operating signal PU3.
The control system 10 is a kind of closed loop control system and deposed with a first summer 141. The first summer 141 subtract the output signal PY of the controlled body 11 from the input signal PR containing a command of the defined values to produce an error signal PE for the master controller 12. The purpose of the whole closed loop control system 10 is to keep the amplitude of the output signal PY to be identical to that of the input signal PR as far as possible, so as to reduce the influence of the interfering signal PW.
Please refer to FIG. 2, which is a step response diagram of a control system according to the prior art. The curve A1 of the input signal of step function command, the curve A2 of the third operating signal and the curve A3 of the output signal are illustrated in FIG. 1.
As shown in FIG. 2, the input signal PR is set as a step function command and processed by the master controller 12 to produce the third operating signal PU3, which will be provided to the controlled body 11. When the control system 11 in FIG. 1 asks for the faster response and minimum error, a larger overshoot will exist in the output signal PY of the controlled body 11.
In addition, since the response of most of the industry process is very slow, it would meet the difficulty when adopting the proportional coefficient, integral coefficient, and a differential coefficient of a differential function to adjust the response of the output signal from the control system.
A user probably needs to wait for several minutes or even several hours for observing the responses produced by the adjusting, and thus it becomes a boring and time-wasting job that tuning the controller by the method of try and error. Sometimes, it is even unable to adjust to meet the system's demands.
In sum, the main motivity of the present application is to reduce the overshoot of the outputting signals of the controlled body while the control system processes with fast response and minimum error, as well as reducing the tuning time and procuring the control system robust.
From the above description, in order to overcome the drawbacks in the prior art, a control system and a method for tuning the system thereof are provided by the inventor via the devoting research and perseverance working.